Aggression and nest spacing in single and mixed species groups of seabirds

When heterospecific seabirds are part of a nesting colony, there may be less opportunity for conspecifics to come in direct contact with each other, resulting in lower intraspecific aggressiveness. To determine if individuals spend less time in aggressive behavior when nesting in conspecific rather than heterospecific groups, we compared the behavior of black skimmers (Rhynchops niger) nesting with gull-billed terns (Sterna nilotica) in three mixed species subcolonies to those of black skimmers in three single species subcolonies. In contrast to our predictions, black skimmers spent significantly less time in aggressive behaviors when nesting in single species subcolonies than when nesting with heterospecifics. Although skimmers in mixed species subcolonies tended to have more aggressive interactions with skimmers than terns, this may be a function of subcolony composition; the proportions of aggressive interactions with conspecifics were similar to the proportions of conspecifics in each subcolony. However, within the mixed species subcolonies, skimmers that nested nearer to terns were involved in aggressive interactions significantly less than skimmers that nested closer to conspecifics. Also, skimmers nested closer to their nearest neighbor when it was a gull-billed tern than when it was another skimmer. Regardless of which species they nested closest to, skimmers were more aggressive towards other skimmers than to terns within the mixed species subcolonies. Distance to nearest neighbor's nest did not differ significantly between the colony types, and did not seem to influence the duration of aggressive activity in the single species subcolonies. In the mixed species subcolonies, however, the time spent in aggressive behavior increased as the distance to nearest neighbor increased. It appears that of the several benefits that have been proposed of mixed species colonies, reduced time spent in conspecific aggression is not among them. However, within a mixed species colony, an individual can reduce time spent in aggressive interactions by nesting near heterospecifics. Received: 16 September 1996 / Accepted: 24 February 1997     

Factors affecting the escape behaviour of juvenile chinstrap penguins, <Emphasis Type="Italic">Pygoscelis antarctica</Emphasis>, in response to human disturbance

Human disturbance can be considered to have similar effects as predation risk for animals. Thus, when disturbed, animal responses are likely to follow the same economic principles used by prey when encountering predators. We simulated predator attacks with different characteristics and in different situations to study the factors that determine the escape response of 1-year-old chinstrap penguins. The results indicate that 1-year-old penguins adjusted their escape behaviour according to the level of risk posed by the researcher acting as a potential predator. When 1-year-old penguins were close to a breeding subcolony, they started to escape later, and fled shorter distances, at lower speeds, and not fleeing directly into the subcolony. This contrasts with their fleeing behaviour far from subcolonies, when penguins fled sooner, for longer, and faster, and in a direction that maximized the distance between themselves and the experimenter, by fleeing directly away from the experimenter. This might suggest the existence of a trade-off between fleeing from the predator and avoiding entering the subcolony where 1-year-old penguins will receive aggressive responses from breeding adults. The type of approach was not important in deciding when to flee. However, penguins did escape for longer distances and faster when approached directly, showing that penguins were able to assess risk level based on predator behaviour. Our findings may have implications for management of penguin colonies visited by tourists. The delimitation of buffer areas and advice on how tourists should behave when approaching penguins might arise from studies of the factors that affect risk assessment of penguins.     

Can redistribution of breeding colonies on a landscape mitigate changing predation danger?

The reproductive success of colonially breeding species depends in part upon a trade‐off between the benefit of a dilution effect against nestling predation within larger colonies and colony conspicuousness. However, there may be no net survivorship benefit of dilution if smaller colonies are sufficiently inconspicuous. This raises the question about how the size distribution of breeding colonies on a landscape might change as the predation danger for nestlings changes. In southwest British Columbia, Canada, bald eagle Haliaeetus leucocephalus populations have increased exponentially at ～5% per year in recent decades and prey upon nestlings of colonial breeding great blue herons Ardea herodias faninni. Motivated by field data on reproductive success in relation to colony size, modeling is used to ask under which circumstances trading off a dilution benefit against colony conspicuousness can improve population reproductive success. That is, which colonial nesting distribution, dispersed and cryptic versus clumped and conspicuous, best mitigates predation danger on nestlings? When predators are territorial, the modeling predicts a dispersed nesting strategy as attack rate increases, but not as predator numbers increase. When predators are non‐territorial, the modeling predicts a dispersed nesting strategy as predator numbers and/or attack rates increase. When predators are both territorial and non‐territorial, colonial nesting within a predator's territory improves reproductive success when attack rates are low. This suggests nesting in association with territorial predators may offer decreased levels of predation when compared with nesting amongst non‐territorial predators. Thus a change in the colony size distribution of colonially breeding species might be anticipated on a landscape experiencing a change in predation danger.     

中国昆明小鼠亚群蛋白质多态性的研究

本文报道采用电泳技术对北京、上海、长春3市的4个中国昆明小鼠(简称KM)实验群体中24个蛋白质标志研究的结果,与我国1981年从美国引进的NIH小鼠进行比较,显示出:(1)KM小鼠亚群间等位基因组成无明显差异,它们间遗传距离为0.008—0.027,与群体封闭时间成正相关;(2)4个KM小鼠群体间聚类分析发现S:KM群体为特殊一类,该结果与KM亚群间下颌骨分析结果相符;(3)KM与Swiss来源的NIH小鼠群体间在E(?)-3、Es-10、Got-2、Glo-1、Gpt-1、和Mpi-1座位上的等位基因组成存在显著差异,它们之间的遗传距离平均值为0.131±0.011,证实中国KM小鼠为非Swiss来源的一个亚种。     

Colony Budding and its Effects on Food Allocation in the Highly Polygynous Ant, Monomorium pharaonis

To advance our understanding of the causes and the consequences of budding (colony multiplication by fragmentation of main nests), we investigated nest movement in the facultatively polydomous Pharaoh ant, Monomorium pharaonis. Demographic data revealed that Pharaoh ants are highly polygynous and have a relatively low worker to queen ratio of 12.86. Budding experiments demonstrated that the number of available bud nests has a significant effect on colony fragmentation and increasing the number of bud nests resulted in smaller colony fragments. The overall distribution among bud nests was uneven, even though there was no evidence that the different life stages and castes partitioned unevenly among the bud nests and the analysis of individual colonies revealed no evidence of an uneven split in any of the colonies. This demonstrates that Pharaoh ants have the ability to exert social control over colony size and caste proportions during budding, which may contribute to their success as an invasive ant. The intensity of nest disturbance had a significant effect on whether or not the ants migrated into bud nests. Major disturbance resulted in the ants abandoning the source nest and migrating to bud nests and minor disturbance did not stimulate the ants to abandon the source nest. The results of the successive budding experiment which allowed the ants the opportunity to bud into progressively smaller nest fragments demonstrate that Pharaoh ants maintain a preferred minimum group size of 469 ± 28 individuals. Food allocation experiments utilizing protein marking revealed that nest fragmentation in Pharaoh ants has no negative impact on intracolony food distribution. Overall, our results suggest that nest units in the Pharaoh ant behave like cooperative, rather than competitive, entities. Such cooperation is most likely facilitated by the fact that individuals in all bud nests are genetically related, remain in close proximity to each other, and may continue to exchange individuals after budding.     

QUANTIFICATION OF TERRESTRIAL HAUL-OUT AND ROOKERY CHARACTERISTICS OF STELLER SEA LIONS

Steller sea lions ( Eumetopias jubatus ) are known to have occupied the same terrestrial haul-out and rookery sites across the North Pacific Rim for centuries, but it is not known why they choose and stay at these locations, or what defines their preferred habitat. Classifying and comparing the shoreline type of haul-outs and rookeries against sites not used by Steller sea lions showed that they preferentially locate their haul-outs and rookeries on exposed rocky shorelines and wave-cut platforms. However, no preference was found for selecting rookeries on sheltered shore types. Shoreline types used less frequently by sea lions included fine-to-medium-grained sand beaches, mixed sand and gravel beaches, gravel beaches, and sheltered rocky shores. Quantifying the shoreline types used by sea lions confirms anecdotal reports of habitat preferences and may prove useful in identifying and protecting sea lion terrestrial habitat, or in forecasting how climate change might affect the distribution of sea lions.     

Can cat predation help competitors coexist in seabird communities?

On oceanic islands, nest site availability can be an important factor regulating seabird population dynamics. The potential for birds to secure a nest to reproduce can be an important component of their life histories. The dates at which different seabird species arrive at colonies to breed will have important consequences for their relative chances of success. Early arrival on the island allows birds to obtain nests more easily and have higher reproductive success. However, the presence of an introduced predator may reverse this situation. For instance, in the sub-Antarctic Kerguelen archipelago, early arriving birds suffer heavy predation from introduced cats. Cats progressively switch from seabirds to rabbits, since the local rabbit population starts to peak after early arriving seabird species have already returned to the colony. When late-arriving birds arrive, cat predation pressure on seabirds is thus weaker. In this paper, we investigate the assumption that the advantage of early nest mnopolization conferred to early arriving birds may be counterbalanced by the cost resulting from predation. We develop a mathematical model representing a simplified situation in which two insular seabird species differ only in their arrival date at the colony site and compete for nesting sites. We conclude that predation may ensure the coexistence of the two bird species or favor the late-arriving species, but only when seasonal variations in predation pressure are large. Interestingly, we conclude that arriving early is only favorable until a given level where high reproductive success no longer compensates for the long exposure to strong predation pressure. Our work suggests that predation can help to maintain the balance between species of different phenologies.     

Predicting resource utilization: the utility of optimal foraging models

Predicting how predation changes communities is an important challenge for ecologists. One view assumes that predictions can be made in terms of behavioural phenomena. Static optimality methods have been used to devise models of prey choice and are thought to have performed well. Two examples from the literature show that models of diet choice have either been applied without first testing them at the individual level, or have been tested in a way that does not fulfil all their assumptions. A discussion of the nature of mathematical models shows why it is dangerous to translate theories into natural language and how important it is to appreciate the limitations on the mathematical functions describing behaviour. A final section discusses behavioural phenomena such as satiation and learning, which are likely to limit the predictive capacities of static optimization models. It is likely that dynamic models are the way forward although they may be harder to apply at the ecological level.     

Factors affecting nest predation on forest songbirds in North America

Nest predation is an important factor in the ecology of passerines and can be a large source of mortality for birds. I provide an overview of factors affecting nest predation of passerines in North America with the goal that it may provide some insight into the ecology and management of woodland birds in the United Kingdom. Although several factors influence productivity, nest success is perhaps the most widely measured demographic characteristic of open-cup-nesting birds, and nest predation is usually the largest cause of nest failure. The identity of predator species, and how their importance varies with habitat and landscape factors, must be known for managers and scientists to design effective conservation plans and place research on nest predation in the appropriate context. Recent studies using video surveillance have made significant contributions to our understanding of the relative importance of different predator taxa in North America. Spatial and temporal variation in nest predation can be better understood when landscapes are placed in a biogeographical context and local habitat and nest-site effects are placed in a landscape context. Low productivity resulting from high nest predation is one of several potential causes of bird population declines in North America and the UK. Although the 'forest fragmentation paradigm' from the eastern US may not apply directly to the UK, thinking about avian demographics from a multiscale perspective, and consideration of factors affecting nest predation with knowledge of the dominant predator species, may provide insight into population declines.     

Behavior of Cape fur seals (Arctocephalus pusillus pusillus) in response to spatial variation in white shark (Carcharodon carcharias) predation risk

Foraging and predation risk are often separated at rookeries of marine central place foragers, thus offering an opportunity to gain insight into how predator‐avoidance shapes the behavior of prey. Here we compare the behavior of Cape fur seals (Arctocephalus pusillus pusillus) at two island rookeries with and without white shark (Carcharodon carcharias) predations, and assess seal behavior in relation to marked spatiotemporal variation in risk at the high‐risk site (Seal Island, South Africa). Our results show that seal behavior at the two sites is comparatively similar in summer, when predation risk is low at both sites, but not in winter. Compared to seals at the “low‐risk” site, seals at Seal Island avoided deep‐water habitat around the island at high risk times and restricted their use of this habitat in favor of safe, shallow waters when engaging in social and thermoregulatory behaviors. Seals increased their frequency of jostling, porpoising, and diving when moving through the danger zone and seals in groups were safer than single individuals. Overall, our results suggest that seal behavior around the high‐risk site is strongly affected by predation risk, and show this rookery to be an excellent predator‐prey system at which to evaluate long‐standing ecological hypotheses.     

Testing habitat copying in breeding habitat selection in a species adapted to variable environments

The habitat copying hypothesis states that animals use the reproductive performance of conspecifics to evaluate habitat quality and choose their future breeding site. We used data from Audouin's Gull Larus audouinii (1992–2003), a species adapted to unpredictable environments, to analyse subcolony (as patch) choice within a colony (small spatial scale). We also assessed the suitability of alternative hypotheses to the habitat copying hypothesis. The probability of subcolonies being reoccupied annually increased with their size (as number of nests), which suggests the existence of group adherence effects. Subcolony growth rate was related to its average reproductive success (or patch reproductive success) in the previous year: the higher the reproductive success in a colony, the higher the probability of growth the following year. However, this last result was obtained without considering the effect of colony size on the response variable because colony size is related to it. Therefore, results suggest at the population level that in this system habitat copying might either be one of the strategies used by the species in selecting its breeding habitat, or one of the possible strategies operating alone. The other strategies are group adherence mechanisms, and also the effect of conspecific attraction. At the individual level we failed to find evidence of habitat copying and only the previous success of an individual affected its fidelity to a subcolony. The importance of the lack of environmental predictability in the system is discussed, as predictability is a prerequisite of habitat copying.     

OCTOSPORIELLA COLORADOENSIS GEN. ET SP. NOV., A NEW TETRASPORALEAN GREEN ALGA FROM TWO COLORADO MOUNTAIN LAKES1

A new green alga, Octosporiella coloradoensis, belonging to the order Tetrasporales, family Tetrasporaceae, is described from Colorado mountain lakes. Colonies are planktonic or attached, the latter often forming loosely aggregated colonial complexes, thus creating an irregularly shaped complex. Individual colonies are spherical and consist of eight subcolonies, with each subcolony having spherically arranged octads of cells. Each vegetative cell bears two pseudoflagella that extend well beyond the colonial sheaths. Cell division is by eleutheroschisis and may be synchronous or asynchronous. Daughter colony formation is apparently coenobic, with each cell in the octad forming new subcolonies of eight cells each. Zoospore formation may precede daughter colony formation but the flagella remain rigid and non-motile. Large akinetes form in response to nutrient depletion. These germinate to produce eight aplanospores which divide to reconstitute a typical colony of Octosporiella. Sexual reproduction was not observed.     

Variable fledging age according to group size: trade-offs in a cooperatively breeding bird

Group living can provide individuals with several benefits, including cooperative vigilance and lower predation rates. Individuals in larger groups may be less vulnerable to predation due to dilution effects, efficient detection or greater ability to repel predators. Individuals in smaller groups may consequently employ alternative behavioural tactics to compensate for their greater vulnerability to predators. Here, we describe how pied babbler (Turdoides bicolor) fledging age varies with group size and the associated risk of nestling predation. Nestling predation is highest in smaller groups, but there is no effect of group size on fledgling predation. Consequently, small groups fledge young earlier, thereby reducing the risk of predation. However, there is a cost to this behaviour as younger fledglings are less mobile than older fledglings: they move shorter distances and are less likely to successfully reach the communal roost tree. The optimal age to fledge young appears to depend on the trade-off between reduced nestling predation and increased fledgling mobility. We suggest that such trade-offs may be common in species where group size critically affects individual survival and reproductive success.     

Balancing Energy Budget in a Central-Place Forager: Which Habitat to Select in a Heterogeneous Environment?

Foraging animals are influenced by the distribution of food resources and predation risk that both vary in space and time. These constraints likely shape trade-offs involving time, energy, nutrition, and predator avoidance leading to a sequence of locations visited by individuals. According to the marginal-value theorem (MVT), a central-place forager must either increase load size or energy content when foraging farther from their central place. Although such a decision rule has the potential to shape movement and habitat selection patterns, few studies have addressed the mechanisms underlying habitat use at the landscape scale. Our objective was therefore to determine how Ring-billed gulls (Larus delawarensis) select their foraging habitats while nesting in a colony located in a heterogeneous landscape. Based on locations obtained by fine-scale GPS tracking, we used resource selection functions (RSFs) and residence time analyses to identify habitats selected by gulls for foraging during the incubation and brood rearing periods. We then combined this information to gull survey data, feeding rates, stomach contents, and calorimetric analyses to assess potential trade-offs. Throughout the breeding season, gulls selected landfills and transhipment sites that provided higher mean energy intake than agricultural lands or riparian habitats. They used landfills located farther from the colony where no deterrence program had been implemented but avoided those located closer where deterrence measures took place. On the other hand, gulls selected intensively cultured lands located relatively close to the colony during incubation. The number of gulls was then greater in fields covered by bare soil and peaked during soil preparation and seed sowing, which greatly increase food availability. Breeding Ring-billed gulls thus select habitats according to both their foraging profitability and distance from their nest while accounting for predation risk. This supports the predictions of the MVT for central-place foraging over large spatial scales.     

Social structure and the defensive role of soldiers in a eusocial bamboo aphid,Pseudoregma bambucicola (Homoptera: Aphididae): A test of the defence-optimization hypothesis

A complete understanding of the evolution of sociality in aphids requires a detailed knowledge of the patterns of soldier investment in their ecology. The eusocial bamboo aphidPseudoregma bambucicola has a morphologically specialized first-instar soldier caste. The proportion of soldiers was positively correlated with colony size. Within a colony, soldiers were evenly distributed among subcolonies; within each subcolony, however, their distribution was biased toward peripheries which were exposed to many predators. Field experiments introducing natural enemies such asEupeodes confrater (Diptera: Syrphidae) andSynonycha grandis (Coleoptera: Coccinellidae) revealed that the survival rate of these predators was negatively correlated with the density of soldiers, suggesting that soldiers can more or less defend their colonies by killing or removing a range of natural enemies. Observations suggest that large mature colonies attract more predators than newly established small colonies and that, within a colony, the predators attack each subcolony regardless of its position on bamboo shoots. This implies the presence of a positive correlation between colony size and predation risk. Thus, the investment in soldiers seems to reflect the attacking pattern of predators within a colony. These results agree with the defence-optimization hypothesis in soldier investment ofP. bambucicola colonies.     

An examination of a compensatory relationship between food limitation and predation in semi-domestic reindeer

A central issue in ecology is to what extent food limitation and predation affect animal populations. We studied how survival and reproductive success was related to the female's size in a population of semi-domesticated reindeer during 2 years where there was a large difference in snowfall during winter. The females were kept within a predator-free enclosure for about 5 weeks during the calving period and thereafter released to their natural summer pastures. Small females were more likely to fail to reproduce and they produced smaller calves than large females. Additionally, small females were more likely to loose their calves due to starvation within the predator-free enclosure and to predators outside the enclosure. Food limitation during the harsh winter appeared to be the major cause of deaths. However, food limitation interacted with predation and led to high calf losses when the females experienced low food availability during the harsh winter. In contrast, predators killed no calves after the mild winter. Apparently, the interaction between predation and food limitation is due to small females favouring their own growth and survival over calf production in summers following harsh winters with food shortage. Our results indicate that a compensatory relationship exists between mortality due food limitation and predation. Thus, the impact of calf predation on reindeer demography and population dynamics may be limited.     

Subcolony variation in phenology and breeding parameters in little auk Alle alle

In seabirds, variation in breeding phenology and success is often induced by macro- and mesoscale fluctuations in oceanographic conditions, which is recordable at the regional or colony scale. Variation in breeding parameters may also exist at the microscale—among discrete breeding aggregations and subcolonies. The aim of this study was to compare breeding phenology and parameters (hatching success, chick survival, chick body mass indices) among little auks (Alle alle) nesting in three subcolonies differing in their microtopographic and microclimatic features, situated in Magdalenefjorden (north-western Spitsbergen). The hatching phenology varied significantly among the subcolonies. This was probably due to the different duration of snow persistence in spring, as nests are occupied as soon as the snow cover melts sufficiently to allow access to them. The earliest hatching was recorded in the subcolony located on steep slopes at low altitude in the vicinity of the fjord, which favours early ice and snow melting in spring. Hatching success differed significantly among subcolonies, which could also have been due to the microclimatic features of the subcolonies. Hatching success was the lowest in the subcolony where birds started to breed while patchy snow was still persisting. Water from the melting snow could have flooded some of the nests. Alternatively, the low hatchability could have been caused by a higher frequency of less experienced breeders (e.g., first-time breeders) among the individuals nesting in this subcolony. Other breeding parameters (chick survival and growth) were generally similar in all the subcolonies.     

Predators and the breeding bird: behavioral and reproductive flexibility under the risk of predation

A growing body of work suggests that breeding birds have a significant capacity to assess and respond, over ecological time, to changes in the risk of predation to both themselves and their eggs or nestlings. This review investigates the nature of this flexibility in the face of predation from both behavioural and reproductive perspectives, and also explores several directions for future research. Most available work addresses different aspects of nest predation. A substantial change in breeding location is perhaps the best documented response to nest predation, but such changes are not always observed and not necessarily the best strategy. Changes in nesting microhabitat (to more concealed locations) following predation are known to occur. Surprisingly little work addresses the proactive avoidance of areas with many nest predators, but such avoidance is probably widespread. Individual birds could conceivably adopt anti‐predator strategies based on the nest predators actually present in an area, but such effects have yet to be demonstrated. In fact, the ways in which birds assess the risk of nest predation is unclear. Nest defence in birds has historically received much attention, but little is known about how it interacts with other aspects of decision‐making by parents. Other studies concentrate on predation risk to adults. Some findings suggest that risk to adults themselves influences territory location, especially relative to raptor nests. An almost completely unexplored area concerns the sorts of social protection from predators that might exist during the breeding season. Flocking typical of the non‐breeding season appears unusual while breeding, but a mated pair may sometimes act as a “flock of two”. Opportunistic heterospecific sociality may exist, with heterospecific protector species associations more prevalent than currently appreciated. The dynamics of singing during the breeding season may also respond to variation in predation risk, but empirical research on this subject is limited. Furthermore, a few theoretical and empirical studies suggest that changes in predation risk also influence the behaviour of lekking males. The major influence of predators on avian life histories is undoubtedly expressed at a broad phylogenetic scale, but several studies hint at much flexibility on an ecological time scale. Some species may forgo breeding completely if the risk of nest predation is too high, and a few studies document smaller clutch sizes in response to an increase in nest predation. Recent evidence suggests that a female may produce smaller eggs rather than smaller clutches following an increase in nest predation risk. Such an increase may also influence decisions about intraspecific brood parasitism. There are no clear examples of changes in clutch/egg size with changes in risk experienced by adults, but parental responses to predators have clear consequences for offspring fitness. Changes in risk to adults may also influence body mass changes across the breeding season, although research here is sparse. The topics highlighted herein are all in need more empirical attention, and more experimental field work whenever feasible.     

The Effect of Moonlight on Scopoli's Shearwater Calonectris diomedea Colony Attendance Patterns and Nocturnal Foraging: A Test of the Foraging Efficiency Hypothesis

Moonlight is known to affect the nocturnal behaviour and activity rhythms of many organisms. For instance, predators active at night may take advantage from increased visibility afforded by the moon, while prey might regulate their activity patterns to become less detectable. Many species of pelagic seabirds attend their colony only at night, in complete darkness, avoiding approaching their nest sites under moonlight. This behaviour has been most often interpreted as an antipredator adaptation (‘predation avoidance’ hypothesis). However, it may also reflect a lower foraging efficiency during moonlit nights (‘foraging efficiency’ hypothesis). Indeed, moonlight may reduce prey availability because preferred seabird prey is known to occur at higher depths in moonlit nights. Using high‐accuracy behavioural information from data loggers, we investigated the effect of moonlight on colony attendance and at‐sea nocturnal foraging in breeding Scopoli's shearwaters Calonectris diomedea. We found that birds departing for self‐feeding trips around the full moon performed longer trips than those departing around the new moon. On nights when the moon was present only partly, nest burrow entrances took place largely in the moonless portion of the night. Moreover, contrary to predictions from the ‘foraging efficiency’ hypothesis, nocturnal foraging activity increased according to moonlight intensity, suggesting that birds increased their foraging activity when prey became more detectable. This study strengthens the idea that colony attendance behaviour is strictly controlled by moonlight in shearwaters, which is possibly related to the perception of a predation risk.     

Effects of predation risk on the nocturnal activity budgets of thin-billed prions Pachyptila belcheri on New Island, Falkland Islands

Predation is a major ecological and evolutionary driver of natural populations, greatly influencing fitness and behaviour of prey species. Small, long-lived petrels are vulnerable to predation at the breeding colonies and are expected to evolve behavioural strategies to minimize predation risks. Using an automatic nest monitoring system and nightly aerial counts, we examined the effect of vegetation cover and moonlight on colony attendance patterns and levels of burrow activity of breeding thin-billed prions, Pachyptila belcheri, on New Island, Falkland Islands. We further investigated how these parameters were related to predation by Falkland skuas. We monitored up to 32 nests in two habitats, one with Tussock grass and one with low vegetation cover. Individuals in both areas were more active at the nest before hatching, and those breeding in the low cover habitat were more active and arrived at the colony earlier, which might reflect an effect of reaction time over predation risk. Nocturnal activity peaks shifted in time as the season progressed, indicating behavioural adjustments to sunrise hours. Moon phase did not affect attendance and activity levels of breeders in either habitat or overall aerial activity, but influenced arrival time at the colony during chick-rearing, individuals arriving later in periods of full moon. Skua capture rates were positively correlated with aerial and nest activity but not with overall breeder attendance and were unaffected by moon phase. Thin-billed prions activity budgets are influenced by environmental parameters that affect their likelihood of being predated.